Self-sealing composition for an inflatable article

ABSTRACT

Self-sealing elastomer composition that can be used especially as a puncture-resistant layer in an inflatable article, comprising: as predominant elastomer, an unsaturated diene elastomer; between 30 and 90 phr of a hydrocarbon resin; and 0 to less than 30 phr of a filler. Also disclosed is an article such as a tire provided with a puncture-resistant layer comprising the self-sealing elastomer composition. The puncture-resistant layer is advantageously combined with an airtight layer, for example based on butyl rubber, so as to form, in the inflatable article, a puncture-resistant airtight laminate.

RELATED APPLICATION

This is a U.S. National Phase Application under 35 USC 371 ofInternational Application PCT/EP2009/005242, filed on Jul. 20, 2009.

This application claims the priority of French patent application No.08/55039 filed Jul. 24, 2008, the entire content of which is herebyincorporated by reference.

FIELD OF THE INVENTION

Such compositions can be used in inflatable articles, especiallyinflatable tires, for sealing off any holes due to perforations inservice.

The present invention relates to self-sealing compositions and to theiruse as puncture-resistant layers in any type of “inflatable” article,that is to say, by definition, any article that takes its useable shapewhen inflated with air.

The invention relates more particularly to the use of such compositionsin inflatable articles, especially inflatable tires, for sealing off anyholes due to perforations in service.

BACKGROUND OF THE INVENTION

Particularly in recent years, tire manufacturers have been makingconsiderable efforts to develop novel solutions to a problem dating fromthe very first use of tired wheels of the inflatable type, namely theproblem of how to allow the vehicle to continue to travel despite aconsiderable or complete loss of pressure of one or more tires. Fordecades, the spare tire was considered to be the only and universalsolution. Then, more recently, the substantial advantages associatedwith its possible omission have become apparent. The concept of“extended mobility” was developed. The associated techniques allow thesame tire to run, depending on certain limits to be respected, after apuncture or a drop in pressure. This makes it possible for example todrive to a breakdown point without having to stop, often in hazardouscircumstances, to fit the spare tire.

Self-sealing compositions that allow such an objective to be achieved,and which by definition are capable of automatically ensuring, that isto say without external intervention, that a tire is sealed in the eventof a perforation of the latter by a foreign body, such as a nail, areparticularly difficult to develop.

To be useable, a self-sealing layer must satisfy many conditions of aphysical and chemical nature. In particular, it must be effective over avery wide range of operating temperatures, and be so throughout thelifetime of the tires. It must be capable of closing off the hole whenthe perforating object remains in place and, when the latter isexpelled, said self-sealing layer must be able to fill the hole and sealthe tire.

Many solutions have been devised but have not been able truly to bedeveloped for vehicle tires, in particular through the lack of stabilityover time or lack of effectiveness under extreme operating temperatureconditions, or else because of difficulties in manufacturing and/orusing these self-sealing compositions.

Thus, to help to maintain good effectiveness at high temperature,document U.S. Pat. No. 4,113,799 (or FR-A-2 318 042) has proposed, asself-sealing layer, a composition comprising a combination of butylrubbers of high and low molecular weights, which are partiallycrosslinked, optionally together with a small amount of a thermoplasticstirene elastomer.

Document U.S. Pat. No. 4,228,839 has proposed, as self-sealing layer fora tire, a rubber compound containing an irradiation-degradable firstpolymer material, such as polyisobutylene, and anirradiation-crosslinkable second polymer material, preferably a butylrubber.

Document U.S. Pat. No. 4,426,468 has also proposed a self-sealingcomposition for a tire, based on a crosslinked butyl rubber of very highmolecular weight.

A known drawback of butyl rubbers is that they suffer from largehysteresis losses (high tan δ level) over a wide temperature range,which drawback has repercussions for the self-sealing compositionsthemselves, with a large increase in hysteresis and an appreciablereduction in rolling resistance of the tires.

Self-sealing compositions based on unsaturated diene elastomers (naturalrubber) have also been described, for the same type of application, inparticular in the patents U.S. Pat. No. 4,913,209, U.S. Pat. No.5,085,942 and U.S. Pat. No. 5,295,525.

These compositions are characterized by the combined presence of a highcontent of hydrocarbon resin as tackifier, always greater than 100 phr,and a large amount of elastomer (isoprene) in the liquid state. Now,such a high resin content, apart from the fact that its incorporationrequires very long kneading of the elastomeric matrix, may also beprejudicial to hysteresis and consequently to the rolling resistance oftires. Furthermore, a large amount of liquid elastomer gives thecomposition a high fluidity, which is a source of other drawbacks,especially a risk of the self-sealing composition creeping when it isused at a relatively high temperature (typically above 60° C.),frequently encountered when certain tires are used.

SUMMARY OF THE INVENTION

One object of the invention is to provide a self-sealing compositionthat requires neither butyl rubber nor large amounts of hydrocarbonresin and liquid elastomer. This composition in an inflatable articlegives better puncture-resistance performance than the self-sealingcompositions of the prior art, particularly when used at a relativelyhigh temperature.

This and other objects are attained according to one aspect of thepresent invention directed to a self-sealing elastomer composition thatcan be used especially as a puncture-resistant layer in an inflatablearticle, said composition comprising at least:

-   -   as predominant elastomer, an unsaturated diene elastomer;    -   between 30 and 90 phr of a hydrocarbon resin; and    -   0 to less than 30 phr of a filler.

Another aspect of the present invention relates to an inflatable articleprovided with a puncture-resistant layer comprising, as self-sealingcomposition, a self-sealing composition according to the invention.

Preferably, the inflatable article according to an embodiment of theinvention, especially a tire, also includes an airtight layer which,when combined with the above puncture-resistant layer, constitutes apuncture-resistant airtight laminate which is particularly advantageouswhen said laminate is placed for example on the internal wall of saidinflatable article or tire.

Tire made in accordance with the present invention can be fitted ontovehicles of the passenger type, SUVs (Sport Utility Vehicles), two-wheelvehicles (especially bicycles and motorcycles), aircraft, or industrialvehicles chosen from vans, “heavy” vehicles, i.e. underground trains,buses, road transport vehicles (lorries, tractors, trailers), off-roadvehicles, such as agricultural or civil engineering machines, and othertransport or handling vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages will be readily understood in the lightof the description and of the exemplary embodiments that follow,together with

FIGS. 1 and 2 relating to these embodiments that show schematically in asimplified manner, without being drawn to a specific scale:

-   -   in radial cross section, an example of a tire using a        self-scaling composition according to the invention (FIG. 1);        and    -   an example of a compounding extruder that can be used to        manufacture a self-sealing composition according to the        invention (FIG. 2).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the present description, unless expressly indicated otherwise, allthe percentages (%) indicated are % by weight.

Moreover, any range of values denoted by the expression “between a andb” represents the range of values starting from more than “a” to lessthan “b” (i.e. with the limits “a” and “b” excluded), whereas any rangeof values denoted by the expression “from a to b” means the range ofvalues starting from “a” and going up to “b”, i.e. including the strictlimits “a” and “b”.

I-1. Self-Sealing Composition

The self-sealing composition or material of the invention is anelastomer composition comprising at least, as predominant elastomer(preferably with a content of more than 50 phr), an unsaturated dieneelastomer and between 40 and 90 phr of a hydrocarbon resin (phr denotingparts by weight per hundred parts of solid rubber). Another essentialfeature of said composition is that it contains no filler or, at thevery most, it contains less than 30 phr thereof.

I-1-A. Unsaturated Diene Elastomer

The term “diene” elastomer or rubber should be understood, as is known,to mean an elastomer (i.e. a homopolymer or a copolymer) at least partlyobtained from diene monomers (i.e. monomers containing two carbon-carbondouble bonds, whether conjugated or not).

These diene elastomers may be put into two categories, namely saturatedand unsaturated. In the present application, the term “unsaturated” (or“essentially unsaturated”) diene elastomer is understood to mean a dieneelastomer that is partly obtained from conjugated diene monomers andhaving a content of repeat units obtained from conjugated dienes ofgreater than 30 mol %. Thus, excluded from this definition are dieneelastomers such as butyl rubbers or copolymers of dienes andalpha-olefins, of the EPDM type, which may be termed “saturated” or“essentially saturated” diene elastomers because of their low content ofdiene-derived repeat units (always less than 15 mol %).

It is preferred to use an unsaturated diene elastomer with a content (inmol %) of repeat units of diene origin (conjugated dienes) of greaterthan 50%, such a diene elastomer being more preferably chosen from thegroup formed by polybutadienes (BR), natural rubber (NR), syntheticpolyisoprenes (IR), butadiene copolymers (for example stirene-butadienerubber or SBR), isoprene copolymers (of course, other than butyl rubber)and blends of these elastomers.

Compared with diene elastomers of the liquid type, the unsaturated dieneelastomer of the composition of the invention is by definition a solid.Preferably, its number-average molecular weight (M_(n)) is between 100000 and 5 000 000, more preferably between 200 000 and 4 000 000 g/mol.The M_(n) value is determined in a known manner, for example by SEC:tetrahydrofuran solvent; 35° C. temperature; 1 g/l concentration; 1ml/min flow rate; solution filtered on a filter of 0.45 μm porositybefore injection; Moore calibration with calibrating polymers (forexample polyisoprene); set of four WATERS columns in series (“STYRAGEL”HMW7, HMW6E, 2 HT6E); differential refractometer (WATERS 2410) detectionand its associated operating software (WATERS EMPOWER).

More preferably, the unsaturated diene elastomer of the composition ofthe invention is an isoprene elastomer. The term “isoprene elastomer” isunderstood to mean, as is known, an isoprene homopolymer or copolymer,in other words a diene elastomer chosen from the group formed by naturalrubber (NR), synthetic polyisoprenes (IR), butadiene-isoprene copolymers(BIR), stirene-isoprene copolymers (SIR), stirene-butadiene-isoprenecopolymers (SBIR) and blends of these elastomers.

This isoprene elastomer is preferably natural rubber or a syntheticcis-1,4-polyisoprene. Among these synthetic polyisoprenes, those havinga content (in mol %) of cis-1,4 bonds of greater than 90%, morepreferably still greater than 95%, especially greater than 98%, arepreferably used.

The above unsaturated diene elastomer, especially an isoprene elastomersuch as natural rubber, may constitute all of the elastomer matrix orthe predominant amount by weight (preferably comprising more than 50%,even more preferably more than 70%) of said matrix when it contains oneor more other elastomers, with a diene or non-diene elastomer, forexample of the thermoplastic elastomer type. In other words, andpreferably, in the composition of the invention, the unsaturated (solid)diene elastomer content, especially isoprene elastomer such as naturalrubber, is greater than 50 phr, more preferably greater than 70 phr.Even more preferably, this content of unsaturated diene elastomer,especially isoprene elastomer such as natural rubber, is greater than 80phr.

According to one particular embodiment, the above unsaturated dieneelastomer, especially when it is an isoprene diene elastomer such asnatural rubber, is the sole elastomer present in the self-sealingcomposition of the invention. However, it could also, according to otherpossible embodiments, be combined with other (solid) elastomers in aminor content by weight, whether these be unsaturated diene elastomers(for example BR or SBR) or even saturated diene elastomers (for examplebutyl), or else elastomers other than diene elastomers, for examplethermoplastic stirene (TPS) elastomers, for example chosen from thegroup formed by stirene/butadiene/stirene (SBS),stirene/isoprene/stirene (SIS), stirene/butadiene/isoprene/stirene(SBIS), stirene/isobutylene/stirene (SIBS),stirene/ethylene-butylene/stirene (SEBS),stirene/ethylene-propylene/stirene (SEPS),stirene/ethylene-ethylene-propylene/stirene (SEEPS) block copolymers andblends of these copolymers.

Surprisingly, this unsaturated diene elastomer, unfilled (or verylightly filled), has proved to be capable, after a thermoplastichydrocarbon resin has been added in the recommended narrow range, offulfilling the function of a highly effective self-sealing composition,as will be explained in detail in the rest of the description.

I-1-B. Hydrocarbon Resin

The second essential constituent of the self-sealing composition is ahydrocarbon resin.

The term “resin” is reserved in the present application, by definition,as known to those skilled in the art, to a compound which is solid atroom temperature (23° C.), as opposed to a liquid plasticizer compoundsuch as an oil.

Hydrocarbon resins are polymers well known to those skilled in the art,essentially based on carbon and hydrogen, which can be used inparticular as plasticizers or tackifiers in polymeric matrices. They areby nature miscible (i.e. compatible) in the contents used with thepolymer compositions for which they are intended, so as to act as truediluents. They have been described for example in the work entitled“Hydrocarbon Resins” by R. Mildenberg, M. Zander and G. Collin (NewYork, VCH, 1997, ISBN 3-527-28617-9), Chapter 5 of which is devoted totheir applications, especially in rubber tires (5.5. “Rubber Tires andMechanical Goods”). They may be aliphatic, cycloaliphatic, aromatic,hydrogenated aromatic, of the aliphatic/aromatic type, i.e. based onaliphatic and/or aromatic monomers. They may be natural or syntheticresins, whether or not based on petroleum (if such is the case, they arealso known as petroleum resins).

Their glass transition temperature (T_(g)) is preferably above 0° C.,especially above 20° C. (usually between 30° C. and 95° C.).

As is known, these hydrocarbon resins may also be termed thermoplasticresins in the sense that they soften when heated and may thus bemoulded. They may also be defined by a softening point or temperature,at which temperature the product, for example in powder form, becomesglutinous. This softening point tends to replace the melting point,which is quite poorly defined, of resins in general. The softening pointof a hydrocarbon resin is generally about 50 to 60° C. higher than theT_(g).

In the composition of the invention, the softening point of the resin ispreferably above 40° C. (in particular between 40° C. and 140° C.), morepreferably above 50° C. (in particular between 50° C. and 135° C.).

Said resin is used in an amount by weight of between 30 and 90 phr.Below 30 phr, the puncture-resistance performance has proved to beinsufficient because of excessive stiffness of the composition, whereasabove 90 phr, the material has insufficient mechanical strength with, inaddition, a risk of its performance being degraded at high temperature(typically above 70° C.). For these reasons, the resin content ispreferably between 40 and 80 phr, even more preferably at least equal to45 phr, especially in the 45 to 75 phr range.

According to a preferred embodiment of the invention, the hydrocarbonresin has at least any one of, and more preferably all, the followingcharacteristics:

-   -   a T_(g) above 25° C.;    -   a softening point above 50° C. (in particular between 50° C. and        135° C.);    -   a number-average molecular weight (M_(n)) of between 400 and        2000 g/mol; and    -   a polydispersity index (I_(p)) of less than 3 (it will be        recalled that I_(p)=M_(w)/M_(n), where M_(w) is the        weight-average molecular weight).

More preferably, this hydrocarbon resin has at least any one of, andmore preferably all, the following characteristics:

-   -   a T_(g) of between 25° C. and 100° C. (especially between 30° C.        and 90° C.);    -   a softening point above 60° C., in particular between 60° C. and        135° C.;    -   a number-average molecular weight M_(n) of between 500 and 1500        g/mol; and    -   a polydispersity index I_(p) of less than 2.

The T_(g) is measured according to the ASTM D3418 (1999) standard. Thesoftening point is measured according to the ISO 4625 standard (“Ringand Ball” method). The macrostructure (M_(w), M_(n) and I_(p)) isdetermined by steric exclusion chromatography (SEC): tetrahydrofuransolvent; 35° C. temperature; 1 g/1 concentration; 1 ml/min flow rate;solution filtered on a filter of 0.45 μm porosity before injection;Moore calibration using polystirene; set of three WATERS columns inseries (“STYRAGEL” HR4E, HR1 and HR0.5); differential refractometer(WATERS 2410) detection and its associated operating software (WATERSEMPOWER).

As examples of such hydrocarbon resins, mention may be made of thosechosen from the group formed by cyclopentadiene (abbreviated to CPD) ordicyclopentadiene (abbreviated to DCPD) homopolymer or copolymer resins,terpene homopolymer or copolymer resins, C₅-cut homopolymer or copolymerresins, and blends of these resins. Among the above copolymer resins,mention may more particularly be made of those chosen from the groupformed by (D)CPD/vinylaromatic copolymer resins, (D)CPD/terpenecopolymer resins, (D)CPD/C₅-cut copolymer resins, terpene/vinylaromaticcopolymer resins, C₅-cut/vinylaromatic copolymer resins and blends ofthese resins.

The term “terpene” includes here, as is known, alpha-pinene, beta-pineneand limonene monomers. It is preferable to use a limonene monomer, acompound which, as is known, can take the form of three possibleisomers: L-limonene (laevogyratory enantiomer), D-limonene(dextrogyratory enantiomer), or else dipentene (the racemic mixture ofthe dextrogyratory and laevogyratory enantiomers). Suitablevinylaromatic monomers are for example: stirene, alpha-methylstirene,ortho-, meta- and para-methylstirene, vinyltoluene,para-tert-butylstirene, methoxystirenes, chlorostirenes,hydroxystirenes, vinylmesitylene, divinylbenzene, vinylnaphthalene andany vinylaromatic monomer derived from a C₉-cut (or more generally a C₈-to C₁₀-cut).

More particularly, mention may be made of resins chosen from the groupformed by (D)CPD homopolymer resins, (D)CPD/stirene copolymer resins,polylimonene resins, limonene/stirene copolymer resins, limonene/D(CPD)copolymer resins, C₅-cut/stirene copolymer resins, C₅-cut/C₉-cutcopolymer resins and blends of these reins.

All the above resins are well known to those skilled in the art and arecommercially available, for example those sold by DRT under the name“Dercolyte” in the case of polylimonene resins, those sold by NevilleChemical Company under the name “Super Nevtac” or sold by Kolon underthe name “Hikorez” as regards C₅-cut/stirene resins or C₅-cut/C₉-cutresins, or else by Struktol under the name “40 MS” or “40 NS” or byExxon Mobil under the name “Escorez” (which are blends of aromaticand/or aliphatic resins).

I-1-C. Filler

The composition of the invention has the essential feature of beingunfilled or only very lightly filled, that is to say containing from 0to less than 30 phr of filler.

The term “filler” is understood here to mean any type of filler, whetherthey are reinforcing (typically nanoparticles with a weight-average sizepreferably of less than 500 nm, especially between 20 and 200 nm) orwhether they are non-reinforcing or inert (typically microparticles witha weight-average size of greater than 1 μm, for example between 2 and200 μm).

These fillers, whether reinforcing or not, are essentially there only togive the final composition dimensional stability, i.e. the minimummechanical integrity required. When the filler is known to bereinforcing vis-à-vis an elastomer, especially an isoprene elastomersuch as natural rubber, it is preferable to use an even smaller amountthereof.

Too high an amount, especially more than 30 phr, no longer makes itpossible to achieve the minimum required flexibility, deformability andcreep properties. For these reasons, the composition of the inventionpreferably contains 0 to less than 20 phr, more preferably 0 to lessthan 10 phr, of filler.

As examples of fillers known to those skilled in the art as reinforcingfillers, mention may in particular be made of carbon black nanoparticlesor a reinforcing inorganic filler, or a blend of these two types offiller.

For example, as carbon blacks, all carbon blacks, especially blacks ofthe HAF, ISAF and SAF types that are conventionally used in tires (thesebeing called tire-grade blacks), are suitable. Among such blacks, thefollowing may more particularly be mentioned: carbon blacks of the 300,600 or 700 series (ASTM grades), such as for example the blacks N326,N330, N347, N375, N683 and N772. Suitable reinforcing inorganic fillersare especially mineral fillers of the silica (SiO₂) type, especiallyprecipitated or pyrogenic silica having a BET surface area of less than450 m²/g, preferably from 30 to 400 m²/g.

As examples of fillers known to those skilled in the art asnon-reinforcing or inert fillers, the following may especially bementioned: microparticles of natural calcium carbonate (chalk) orsynthetic calcium carbonate, synthetic or natural silicates (such askaolin, talc or mica), milled silicas, titanium oxides, aluminas or evenaluminosilicates. As examples of lamellar fillers, graphite particlesmay in particular be mentioned. Pigmenting or coloured fillers could beadvantageously used to colour the composition according to the desiredcolour.

The physical state of the filler does not matter—it could be in the formof powder, microspheres, granules or beads, or any other suitabledensified form. Of course, the term “filler” is also understood to meanmixtures of various reinforcing and/or non-reinforcing, fillers.

A person skilled in the art will know, in the light of the presentdescription, how to adjust the formulation of the self-sealingcomposition so as to achieve the desired property levels and to adaptthe formulation to the envisaged specific application.

According to one particular advantageous embodiment of the invention, ifa reinforcing filler is present in the composition of the invention, itscontent is preferably less than 5 phr (i.e. between 0 and 5 phr), inparticular less than 2 phr (i.e. between 0 and 2 phr). Such contentshave proved to be particularly favourable to the process formanufacturing the composition of the invention, while still providing itwith excellent self-sealing performance. More preferably a contentbetween 0.5 and 2 phr is used, particularly when the filler is carbonblack.

I-1-D. Various Additives

The base constituents described above, namely the unsaturated dieneelastomer, the hydrocarbon plasticizing resin and the optional filler,are sufficient in themselves for the self-sealing composition tocompletely fulfil its puncture-resistance function within the inflatablearticles in which it is used.

However, various other additives may be added, typically in a smallamount (preferably with contents of less than 20 phr, more preferablyless than 15 phr), such as for example protection agents, such as UVstabilizers, antioxidants or antiozonants, various other stabilizers,and colouring agents that can be advantageously used to colour theself-sealing composition. Depending on the intended application, fibres,in the form of short fibres or pulp, could optionally be added to givethe self-sealing composition greater cohesion.

According to a preferred embodiment of the invention, the self-sealingcomposition further includes a system for crosslinking the unsaturateddiene elastomer. This crosslinking system is preferably a sulphur-basedcrosslinking system, in other words what is called a “vulcanization”system.

Preferably, the sulphur-based vulcanization system includes, asvulcanization activator, a guanidine derivative, i.e. a substitutedguanidine. Substituted guanidines are well known to those skilled in theart (see for example WO 00/05300) and non-limiting examples that may bementioned include: N,N′-diphenylguanidine (abbreviated to DPG),triphenylguanidine and di-o-tolylguanidine. Preferably, DPG is used.

In this vulcanization system, to obtain optimum self-sealing performancethe sulphur content is preferably between 0.1 and 1.5 phr, in particularbetween 0.2 and 1.2 phr (for example between 0.2 and 1.0 phr) and theguanidine derivative content is itself between 0 and 1.5 phr, inparticular between 0 and 1.0 phr (especially in the 0.2 to 0.5 phrrange).

Said system does not require a vulcanization accelerator to be present.According to a preferred embodiment, the composition may thereforecontain no such accelerator, or at the very most it may contain lessthan 1 phr, more preferably less than 0.5 phr, thereof. According toanother advantageous embodiment, the above vulcanization system maycontain no zinc or zinc oxide (these being known as vulcanizationactivators).

According to another possible embodiment of the invention, a sulphurdonor may be used instead of sulphur itself. Sulphur donors are wellknown to those skilled in the art. Typically, the amount of such asulphur donor will preferably be adjusted to be between 0.5 and 10 phr,more preferably between 1 and 5 phr, so as to achieve the preferredequivalent sulphur contents indicated above.

After curing, a vulcanization system as described above gives thecomposition sufficient cohesion, without truly vulcanizing it: theamount of crosslinking, which can be measured using a conventionalswelling method known to those skilled in the art, is in fact close tothe detection threshold.

Apart from the elastomers described above, the self-sealing compositioncould also contain, again as a minor weight fraction relative to theunsaturated diene elastomer, polymers other than elastomers such as, forexample, thermoplastic polymers compatible with the unsaturated dieneelastomer.

I-2. Manufacture of the Self-Sealing Composition

The composition described above may be manufactured by any appropriatemeans, for example by compounding and/or kneading in blade mixers oropen mills, until an intimate homogeneous mixture of its variouscomponents has been obtained.

However, the following manufacturing problem may arise: in the absenceof any filler, or at least an appreciable amount of filler, thecomposition is not very cohesive. This lack of cohesion may be such thatthe tack of the composition, due moreover to the presence of arelatively high hydrocarbon resin content, is not compensated for andcauses some of the composition to be carried away—it follows that thereis a risk of it sticking undesirably on the compounding tools, whichsituation may be unacceptable under industrial operating conditions.

To alleviate the above problems, the self-sealing composition of theinvention, when it includes a vulcanization system, may be preparedusing a process comprising the following steps:

-   -   a) firstly a masterbatch comprising at least one unsaturated        diene elastomer and between 30 and 90 phr of hydrocarbon resin        is manufactured, by compounding these various components in a        mixer at a temperature or up to a temperature called the “hot        compounding temperature” or “first temperature” which is above        the softening point of the hydrocarbon resin; and    -   b) then at least the crosslinking system is incorporated into        said masterbatch, by compounding everything, in the same mixer        or in a different mixer, at a temperature or up to a temperature        called the “second temperature” which is maintained below 100°        C., in order to obtain said self-sealing composition.

The above first and second temperatures are of course those of themasterbatch and of the self-sealing composition respectively, thesebeing temperatures measurable in situ and not the set temperatures ofthe mixers themselves.

The term “masterbatch” should be understood here to mean, by definition,a compound comprising at least the diene elastomer and the hydrocarbonresin, namely the precursor compound for the final self-sealingcomposition ready to be used.

Optionally, various additives may be incorporated into this masterbatch,whether these are intended for the masterbatch proper (for example astabilizing agent, a colorant, a UV stabilizer, an antioxidant, etc.) orfor the final self-sealing composition for which the masterbatch isintended.

Such a process has proved to be particularly suitable for rapidlymanufacturing, under industrially acceptable operating conditions, aneffective self-sealing composition based on diene elastomers andhydrocarbon resins, which composition may have high hydrocarbon contentswithout requiring in particular the use of an elastomer in the liquidstate.

It is during the hot compounding step a) that the diene elastomer isbrought into contact with the hydrocarbon resin in order to manufacturethe masterbatch. In the initial state, that is to say before it comesinto contact with the elastomer, the resin may be in the solid state orin the liquid state. Preferably, for better compounding, the solid dieneelastomer is brought into contact with the hydrocarbon in the liquidstate. To do this, it suffices to heat the resin to a temperature aboveits softening point. Depending on the type of hydrocarbon resin used,the hot compounding temperature is typically above 70° C., usually above90° C., for example between 100° C. and 150° C.

Step b) of incorporating the crosslinking system is carried out at atemperature preferably below 80° C., of preferably below the softeningpoint of the resin. Thus, depending on the type of hydrocarbon resinused, the compounding temperature of step b) is preferably below 50° C.,more preferably between 20° C. and 40° C.

If necessary, an intermediate step of cooling the masterbatch may beinserted between the above steps a) and b) so as to bring themasterbatch temperature to below 100° C., preferably below 80° C.,especially below the softening point of the resin, before introduction(step b)) of the crosslinking system into the masterbatch preparedbeforehand.

When a filler such as carbon black is used, it may be introduced duringstep a), i.e. at the same time as the unsaturated diene elastomer andthe hydrocarbon resin, or else during step b), i.e. at the same time asthe crosslinking system. It has been found that a very small proportionof carbon black, preferably between 0.5 and 2 phr, further improves thecompounding and the manufacture of the composition, and also its finalextrudability.

Step a) of manufacturing the masterbatch is preferably carried out in acompounding screw extruder as shown schematically for example in asimplified manner in FIG. 2.

FIG. 2 shows a compounding screw extruder (20) essentially comprising anextrusion screw (21) (for example a single-screw compounding extruder),a first metering pump (22) for the diene elastomer (which is solid) anda second metering pump (23) for the resin (which is solid or liquid).The metering pumps (22, 23) are used to raise the pressure in theextruder while still controlling the metering and the initialcharacteristics of the materials, before separating the meteringfunction (for elastomer and resin) from the compounding function, whilefurthermore providing better control of the process.

The products, driven by the extrusion screw, are intimately compoundedunder the very high shear provided by the rotation of the screw, thusprogressing through the mixer, for example up to a part (24) called the“chopper-homogenizer”, after which zone the final masterbatch (25) thusobtained, progressing in the direction of the arrow (F), is finallyextruded through a die (26) for extruding the product to the desireddimensions.

The masterbatch thus extruded, ready to be used, is then transferred andcooled, for example on an external mixer of the two-roll open mill typefor introducing the crosslinking system and the optional filler, thetemperature within said external mixer being kept below 100° C.,preferably below 80° C. and more preferably below the softening point ofthe resin. Advantageously, the rolls of the above open mill are cooled,for example by circulating water, to a temperature below 40° C.,preferably to below 30° C., so as to avoid any undesirable sticking ofthe composition to the walls of the mill.

It is possible for the masterbatch output by the extrusion device (20)to be formed directly, so as to make it easier to transport to and/orplace in the external mixer. It is also possible for the two-roll openmill to be continuously fed.

Thanks to the preferred process and specific devices described above, itis possible to prepare the composition of the invention undersatisfactory industrial conditions without running the risk ofcontaminating the tools due to undesirable sticking of the compositionon the walls of the mixers.

I-3. Use of the Self-Sealing Composition as Puncture-Resistant Layer

The self-sealing composition or material described above is an elasticcompound which is solid (at 23° C.) and is characterized in particular,thanks to its specific formulation, by a very high flexibility anddeformability.

It may be used as a puncture-resistant layer in any type of “inflatable”article, that is to say, by definition, any article that takes itsuseable form when inflated with air.

Examples of such inflatable articles that may be mentioned includeinflatable boats and balloons or balls used for games or sport.

It is particularly well suited to use as a puncture-resistant layer inan inflatable article, finished or semifinished product, made of rubber,most particularly in a tire for a motor vehicle, such as a vehicle ofthe two-wheeled type, a passenger or industrial vehicle, or anon-automobile vehicle such as a bicycle.

Such a puncture-resistant layer is preferably placed on the internalwall of the inflatable article, completely or at least partly coveringit, but it may also be completely integrated into its internalstructure.

The thickness of the puncture-resistant layer is preferably greater than0.3 mm, more preferably between 0.5 mm and 10 mm (in particular between1 and 5 mm).

It will be readily understood that, in the specific fields ofapplication, the dimensions and the pressures involved and the method ofimplementing the invention may vary, the puncture-resistant layer thencomprising several preferred thickness ranges. Thus, for example, fortires of the passenger vehicle type, said puncture-resistant layer mayhave a thickness of at least 0.5 mm, preferably between 1 and 5 mm.According to another example, for heavy or agricultural vehicle tires,the preferred thickness may be between 1 and 6 mm. According to anotherexample, for vehicle tires in the civil engineering or aircraft field,the preferred thickness may be between 2 and 10 mm. Finally, accordingto another example, for bicycle tires, the preferred thickness may bebetween 0.4 and 2 mm.

The self-sealing composition described here has the advantage ofsuffering practically no adverse effect in terms of rolling resistance,over a very wide operating temperature range of the tires, compared witha tire not having such a self-sealing layer. Compared with the usualself-sealing compositions, the risks of excessive creep during use at arelatively high temperature (typically above 60° C.), as is frequentlyencountered when using certain tires, are appreciably reduced.

Of course, the invention applies to cases in which the self-sealingcomposition described above is used in a tire or any other inflatablearticle without necessarily being combined with an airtight layer.

However, according to a particular preferred embodiment of theinvention, the self-sealing composition is combined with at least asecond, airtight layer in order to form a multilayer laminate, which isself-sealing and airtight, and which can be used in particular as aninternal wall of an inflatable article such as a tire.

The second layer of the laminate may comprise any type of material thatcan fulfil the function of an airtight film (or more generally agastight film), whether this is for example a metallic material or apolymeric material. Preferably, this airtight layer has a thickness ofgreater than 0.05 mm, more preferably between 0.05 and 6 mm (for examplefrom 0.1 to 2 mm).

According to a preferred embodiment, this airtight second layercomprises a butyl rubber composition. The term “butyl rubber” should beunderstood, as is known, to mean an isobutylene/isoprene copolymer(abbreviated to IIR), and also halogenated, preferably chlorinated orbrominated, versions of this type of copolymer. Preferably, the butylrubber is a halogenated butyl rubber or a blend of halogenated andnon-halogenated butyls. The butyl rubber may be used by itself or incombination with one or more other elastomers, especially dieneelastomers, such as for example natural rubber or a syntheticpolyisoprene. The airtight composition also includes the variousadditives that are usually present in the airtight layers known to thoseskilled in the art, such as reinforcing fillers, such as carbon black,lamellar fillers improving the sealing (e.g. phyllosilicates such askaolin, talc, mica, clays or modified clays (“organ clays”)), protectiveagents such as antioxidants or antiozonants, a crosslinking system (forexample based on sulphur or peroxide) and various processing aids orother stabilizers.

The two layers of the above laminate may be joined together by anyappropriate means, for example by a simple heat operation, preferablyunder pressure (for example for several minutes at 150° C. under apressure of 16 bar) using various adhesives or by inserting a thirdadhesive layer to stick the two other layers together.

II. Exemplary Embodiment of the Invention

The self-sealing composition and the multilayer laminate described abovemay advantageously be used in tires for all types of vehicle,particularly in tires for passenger vehicles liable to run at very highspeed or tires for heavy industrial vehicles such as heavy goodsvehicles liable to run and operate under particularly high internaltemperature conditions.

To give an example, the appended FIG. 1 shows very schematically(without complying to a specific scale), a radial cross section througha tire according to the invention.

This tire 1 comprises a crown 2 reinforced by a crown reinforcement orbelt 6, two sidewalls 3 and two beads 4, each of these beads 4 beingreinforced with a bead wire 5. The crown 2 is surmounted by a tread (notshown in this schematic figure). A carcass reinforcement 7 is woundaround the two bead wires 5 in each bead 4, the upturn 8 of thisreinforcement 7 lying for example towards the outside of the tire 1,which here is shown fitted onto its rim 9. The carcass reinforcement 7consists, as is known per se, of at least one ply reinforced by cords,called “radial” cords, for example textile or metal cords, i.e. thesecords are arranged practically parallel to one another and extend fromone bead to the other so as to make an angle of between 80° and 90° withthe circumferential mid-plane (the plane perpendicular to the rotationaxis of the tire, which lies at mid-distance between the two beads 4 andpasses through the middle of the crown reinforcement 6).

The tire 1 is characterized in that its internal wall includes amultilayer laminate (10) comprising at least two layers (10 a, 10 b),which is self-sealing thanks to its first layer (10 a) and airtightthanks to its second layer (10 b).

According to a preferred embodiment of the invention, the two layers (10a, 10 b) cover substantially the entire internal wall of the tire,extending from one sidewall to the other, at least up to level with therim gutter when the tire is in the fitted position. According to otherpossible embodiments, the layer 10 a could however cover only a portionof the airtight zone (layer 10 b), for example only the crown zone ofthe tire, or it could extend at least from the crown zone to theshoulders or to the mid-point (the equator) of said tire.

According to another preferred embodiment, the laminate is placed insuch a way that the self-sealing first layer (10 a) is radially theoutermost layer in the tire relative to the other layer (10 b), shownschematically in the appended figure. In other words, the self-sealinglayer (10 a) covers the airtight layer (10 b) on the side facing theinternal cavity 11 of the tire 1. Another possible embodiment is that inwhich this layer (10 a) is the radially most internal layer, thereforeplaced between the sealed layer (10 b) and the rest of the structure ofthe tire 1.

In this example, the layer 10 b (with a thickness of 0.7 to 0.8 mm) isbased on butyl rubber and has a conventional formulation for an “innerliner” which usually defines, in a conventional tire, the radiallyinternal face of said tire, intended to protect the carcassreinforcement from air diffusing from the internal space of the tire.This airtight layer 10 b therefore enables the tire 1 to be inflated andto hold pressure. Its sealing properties enable it to guarantee arelatively low rate of pressure loss, enabling the tire to be keptinflated, in a normal operating state, for a sufficient duration,normally for several weeks or several months.

The layer 10 a itself consists of a self-sealing composition accordingto the invention comprising the two essential constituents, namelynatural rubber (100 phr) and a hydrocarbon resin “Escorez 2101” fromExxon Mobil (having a softening point of about 90° C.) and in a weightfraction of about 50 phr; it also contains a very small amount (1 phr)of carbon black (N772).

The above self-sealing composition was prepared using a single-screw (40L/D) extruder as shown schematically in FIG. 2 (which has already beencommented upon). The two base constituents (NR and resin) werecompounded at a temperature (between 100 and 130° C.) above thesoftening point of the resin. The extruder used had two different feeds(hoppers) (one for the NR and the other for the resin) and a pressurizedliquid injection pump for the resin (injected at a temperature of about130° C.). When the elastomer and the resin had thus been intimatelycompounded, it was found that the undesirable tack of the compositionwas very significantly reduced.

The above extruder was provided with a die for extruding the masterbatchto the desired dimensions into a two-roll open mill for the finalincorporation of the other constituents, namely the vulcanization systembased on sulphur (for example 0.5 or 1.2 phr) and DPG (for example 0.3phr) and carbon black (with a content of 1 phr), at low temperaturemaintained below +30° C. (by cooling the rolls with circulating water).

The layer 10 a, placed therefore between the layer 10 b and the cavity11 of the tire, gives the tire effective protection against loss ofpressure due to accidental perforations, enabling these perforations tobe automatically sealed off.

If a foreign body, such as a nail, passes through the structure of thetire, for example a wall, such as a sidewall 3 or the crown 6 of thetire 1, the composition serving as self-sealing layer is subjected toseveral stresses. In reaction to these stresses, and thanks to itsadvantageous deformability and elasticity properties, said compositioncreates an impermeable contact zone around the body. It does not matterwhether the contour or the profile of said body is uniform or regular,the flexibility of the self-sealing composition enables it to beinsinuated into openings of very small size. This interaction betweenthe self-sealing composition and the foreign body seals the zoneaffected by said body.

In the event of the foreign body being removed, whether accidentally orintentionally, a perforation remains, this being liable to create arelatively large leak, depending on its size. The self-sealingcomposition, exposed to the hydrostatic pressure, is sufficiently softand deformable to seal off, by being deformed, the perforation,preventing the inflation gas from leaking. In particular in the case ofa tire, it has been shown that the flexibility of the self-sealingcomposition enables the forces of the surrounding walls to be withstoodwithout any problems, even during phases in which the loaded tiredeforms when running.

The tire provided with its puncture-resistant layer (10 a) as describedabove may be produced before or after vulcanization (or curing).

In the first case (i.e. before the tire is cured), the self-sealingcomposition is simply applied in a conventional manner at the desiredplace, so as to form the layer 10 a. The vulcanization operation is thencarried out conventionally.

An advantageous manufacturing variant, for a person skilled in the artof manufacturing tires, would for example consist, during a first step,in depositing the self-sealing composition flat, directly on atire-building drum, in the form of a skim of suitable thickness (forexample 2 to 6 mm), before being covered with the airtight layer,followed by the rest of the structure of the tire, using manufacturingtechniques well known to those skilled in the art. This type of processalso allows the second embodiment, in which the sealing layer 10 b isthe radially outermost layer, to be easily produced.

In the second case (i.e. after the tire is cured), the self-sealingcomposition is applied to the inside of the cured tire by anyappropriate means, for example by bonding, by spraying or byextrusion-blowing a film of appropriate thickness.

During trials, tires of the passenger car type, of 205/55 R16 size, ofthe “Michelin, Energy 3 brand” were tested. The internal wall of thetires (already including the airtight layer (10 b)) was covered with theself-sealing layer (10 a) described above, having a thickness of 3 mm,and then the tires were vulcanized.

On one of the tires, when fitted and inflated, five perforations 5 mm indiameter were produced through the tread and the crown block on the onehand, and through the sidewalls on the other, using punches that wereimmediately removed.

Unexpectedly, this tire withstood being rotated at 150 km/h on a rollingdrum under a nominal load of 400 kg without loss of pressure for morethan 1500 km, after which distance the rolling step was stopped.

On another tire, the test was carried out in the same way but this timeleaving the perforating objects in place for one week. The sameexcellent result was obtained.

Without the self-sealing composition and under the same conditions asabove, the tire thus perforated loses its pressure in less than oneminute, becoming completely unsuitable for rolling.

The invention claimed is:
 1. An inflatable article provided with apuncture-resistant layer comprising a self-sealing elastomercomposition, said composition comprising: as predominant elastomer, anunsaturated diene elastomer; between 40 and 80 phr of a hydrocarbonresin; and 0 to less than 30 phr of a filler; wherein the hydrocarbonresin has a softening point above 50° C., a glass transition temperature(Tg) above 25° C., a number-average molecular weight (Mn) of between 400and 2000 g/mol, a polydispersity index (Ip) of less than 3 (whereIp=Mw/Mn, and Mw is a weight-average molecular weight), the inflatablearticle has an internal wall, and the puncture-resistant layer isdeposited on the internal wall of the inflatable article.
 2. The articleaccording to claim 1, wherein the unsaturated diene elastomer isselected from the group consisting of polybutadienes, natural rubber,synthetic polyisoprenes, butadiene copolymers, isoprene copolymers, andblends of these elastomers.
 3. The article according to claim 2, whereinthe unsaturated diene elastomer is an isoprene elastomer selected fromthe group consisting of natural rubber, synthetic polyisoprenes, andblends of these elastomers.
 4. The article according to claim 1, whereinthe unsaturated diene elastomer content is greater than 50 phr in theself-sealing elastomer composition.
 5. The article according to claim 1,wherein the isoprene elastomer is the sole elastomer of the self-sealingelastomer composition.
 6. The article according to claim 1, wherein thenumber-average molecular weight of the diene elastomer is between 100000 and 5 000 000 g/mol.
 7. The article according to claim 1, whereinthe hydrocarbon resin content is in the 45 to 75 phr range in theself-sealing elastomer composition.
 8. The article according to claim 1,wherein the hydrocarbon resin has a Tg above 25° C. and no greater than+100° C.
 9. The article according to claim 1, wherein the hydrocarbonresin is selected from the group consisting of cyclopentadiene (CPD)homopolymer or copolymer resins, dicyclopentadiene (DCPD) homopolymer orcopolymer resins, terpene homopolymer or copolymer resins, C₅-cuthomopolymer or copolymer resins, and blends of these resins.
 10. Thearticle according to claim 9, wherein the hydrocarbon resin is selectedfrom the group consisting of DCPD homopolymer resins, DCPD/styrenecopolymer resins, polylimonene resins, limonene/styrene copolymerresins, limonene/DCPD copolymer resins, C₅-cut/styrene copolymer resins,C₅-cut/C₉-cut copolymer resins, and blends of these resins.
 11. Thearticle according to claim 1, wherein the amount of the filler in theself-sealing elastomer composition is 0 to less than 20 phr.
 12. Thearticle according to claim 1, wherein the filler is carbon black. 13.The article according to claim 12, wherein the amount of carbon black isless than 5 phr.
 14. The article according to claim 12, wherein theamount of carbon black is between 0.5 and 2 phr.
 15. The articleaccording to claim 1, wherein the self-sealing elastomer compositionfurther comprises a vulcanization system.
 16. The article according toclaim 15, wherein the vulcanization system is based on sulphur and aguanidine derivative.
 17. The article according to claim 16, wherein theguanidine derivative is diphenylguanidine (DPG).
 18. The articleaccording to claim 16, wherein the vulcanization system comprisesbetween 0.1 and 1.5 phr of sulphur and between 0 and 1.5 phr ofguanidine derivative.
 19. The article according to claim 18, wherein thevulcanization system comprises between 0.2 and 1.2 phr of sulphur andbetween 0 and 1.0 phr of guanidine derivative.
 20. The article accordingto claim 1, wherein the self-sealing composition is in the form of apuncture-resistant layer having a thickness of greater than 0.3 mm. 21.The article according to claim 20, wherein the puncture-resistant layerhas a thickness of between 0.5 mm and 10 mm.
 22. The article accordingto claim 1, which is a rubber article.
 23. The article according toclaim 22, which is a tire.
 24. The article according to claim 1, whereinthe puncture-resistant layer is combined with an airtight layer thusconstituting an airtight self-sealing laminate.
 25. The articleaccording to claim 24, wherein the airtight layer is based on butylrubber.
 26. An inflatable article provided with a puncture-resistantlayer consisting of a self-sealing elastomer composition, saidcomposition comprising: as a sole elastomer, an unsaturated dieneelastomer with a number-average molecular weight between 100 000 and 5000 000 g/mol; between 30 and 90 phr of a hydrocarbon resin; and 0 toless than 30 phr of a filler; wherein the hydrocarbon resin has asoftening point above 40° C., a number-average molecular weight (Mn) ofbetween 400 and 2000 g/mol, a polydispersity index (Ip) of less than 3(where Ip=Mw/Mn, and Mw is a weight-average molecular weight), theinflatable article has an internal wall, the puncture-resistant layer isdeposited on the internal wall of the inflatable article, and theunsaturated diene elastomer is selected from the group consisting ofpolybutadienes, natural rubber, synthetic polyisoprenes, butadienecopolymers, isoprene copolymers, and combinations thereof.
 27. Theinflatable article of claim 26 wherein the unsaturated diene elastomeris an isoprene elastomer.
 28. The inflatable article of claim 27 whereinthe isoprene elastomer is selected from a group consisting of naturalrubber, synthetic polyisoprenes, and combinations thereof.